ibmvnic: Allocate max queues stats buffers

To avoid losing any stats when the number of sub-crqs change, allocate
the max number of stats buffers so a stats buffer exists all possible
sub-crqs.

Signed-off-by: Nathan Fontenot <nfont@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>